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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter37 Configuring EtherChann els and Link-State Tracking
Understanding EtherChannels
PAgP sends and receives PAgP PDUs only from ports that are up and have PAgP enabled for the auto
or desirable mode.
Link Aggregation Control Protocol
The LACP is defined in IEEE 802.3ad and enables Cisco switches to manage Ethernet channels between
switches that conform to the IEEE 802.3ad protocol. LACP facilitates the automatic creation of
EtherChannels by exchanging LACP packets between Ethernet ports.
By using LACP, the switch or switch stack learns the identity of partners capable of supporting LACP
and the capabilities of each port. It then dynamically groups similarly configured ports into a single
logical link (channel or aggregate port). Similarly configured ports a re grouped based on hardware,
administrative, and port parameter constraints. For example, LACP groups the ports with the same
speed, duplex mode, native VLAN, VLAN range, and trunking status and type. After grouping the links
into an EtherChannel, LACP adds the group to the spanning tree as a single switch port.

LACP Modes

Table37-2 shows the use r-configurable EtherChannel LACP modes for the channel-group interface
configuration command.
Both the active and passive LACP modes enable ports to negotiate with partner ports to an
EtherChannel based on criteria such as port speed and, for Lay er 2 EtherChannels, trunking state and
VLAN numbers.
Ports can form an EtherChannel when they are in different LACP modes as long as the modes are
compatible. For example:
•A port in the active mode can form an EtherChannel with another port that is in the active or passive
mode.
•A port in the passive mode cannot form an EtherChannel with another port that is also in the passive
mode because neither port starts LACP negotiation.

LACP Interaction with Other Features

The DTP and the CDP send and receive packets over the physical ports in the EtherChannel. Trunk ports
send and receive LACP PDUs on the lowest numbered VLAN.
Table37-2 EtherChannel LACP Modes
Mode Description
active Places a port into an active negotiating state in which the port starts negotiations with other
ports by sending LACP packets.
passive Places a port into a passive negotiating state in which the port responds to LACP packets
that it receives, but does not start LACP packet negotiation. This setting minimizes the
transmission of LACP packets.